Sintered products of inorganic non-metallic or metallic powders have been used in structural parts, wear parts, semiconductor substrates, printed circuit boards, electrically insulating parts, high hardness and high precision machining materials (e.g., cutting tools, dies, bearings, etc.), functional materials such as grain boundary capacitors, humidity sensors, and precision sinter molding materials, among other applications.
When inorganic non-metallic or metal powders are sintered to produce a product (often with the application of pressure), the starting particles are often blended with additives for such purposes as lowering the sintering/consolidation temperature and/or pressure, or modifying/improving the physical or mechanical properties of the resultant compact.
The current state of the art in metals and ceramics processing is to mill or blend additives and modifiers using a ball mill or attrition milling technology. More recent inventions utilize coprecipitation, atomization, or self-assembly to improve distribution and reaction controllability of these composite materials.
Applicant has proposed in a prior application a method for coating fine particles with coatings of ceramic and metallic materials. This is a process for applying coatings to particles in a continuous (or discontinuous, depending on application), pore-free manner. The current invention relates to the design and/or composition of matter for metal and/or ceramic particles to which have been applied a surface modifying layer or layers. When the core and claddings posses highly different properties, including electronegativity, free energy of formation, or oxidizing potential, the combination can be made to react in a controlled fashion in response to the imposition of an external stimulus, such as shear (e.g., impact), thermal (high temperature ignition), or catalysis or activation (addition of an electrolyte such as salt water or acid).
Umeya (U.S. Pat. No. 5,489,449) discloses the use of ultrafine sintering aids dispersed/coated onto the surface of ceramic particles using precipitation techniques. Umeya further describes a process for forming ultrafine ceramic particles through gas-phase nucleation which are then deposited onto the surfaces of ceramic particles. This process has inherent limitations in that it does not provide for a continuous, uninterrupted coating on the ceramic surface, and does not address reaction/interaction of the sintering aid with the particle itself. Umeya uses chemical reduction of copper oxide and other precursors, and the techniques described are not applicable to reactive systems due to temperature and chemical environments, and the reactivity of magnesium, aluminum, and other reactive metals
Beane (U.S. Pat. Nos. 5,614,320 and 5,453,293) and others disclose a related process for controlling the end thermal (CTE, thermal conductivity) properties of a material by forming a coated particle having two materials that have distinctly different intrinsic properties. Such process allows for the production of a material with a property controlled by rules of mixture relationships between the limits set by the two materials consisting of the coating material and the core particle material.
Lee et al. (U.S. Pat. No. 4,063,907) discloses a process for producing smeared metal coatings on diamond particles to produce a chemically bonded coating on the diamond particles to improve adhesion in a matrix material.
Kuo et al. (U.S. Pat. No. 5,008,132) discloses a process for applying a titanium nitride coating to silicon carbide particles using a diffusion barrier interlayer to improve the wettability and to inhibit the reaction of the silicon carbide particles in a titanium metal matrix.
Gabor et al. (U.S. Pat. No. 5,405,720) discloses the use of refractory carbide and nitride coatings on abrasive particles.
Yajima et al. (U.S. Pat. No. 4,134,759) discloses the use of certain coatings on continuous SiC ceramic fibers that have an exterior carbon coating that increases the wettability in aluminum and aluminum alloys.
Wheeler et al. (U.S. Pat. No. 5,171,419) discloses the use of CoW and NiW interlayers on ceramic fibers for this purpose.
Chance et al. (U.S. Pat. No. 5,292,477) discloses an atomizing process for producing uniform distributions of grain growth control additives throughout the bulk of a particle.
Quick et al. (U.S. Pat. No. 5,184,662) disclose a related process for forming metal/ceramic composite particles that have a continuous cladding of the metal.
In each of these prior art references, the disclosures do not include the controlling of particle reactivity.